Question

Steam saturated at 70 kPa is condensing on a ¾ in. Sch 40 vertical tube 1 ft. long and a surface temperature of 90 deg C. Calculate the average heat-transfer coefficient. Express your answer in AES units. (Note: Use the film-condensation coefficient for vertical surfaces)

Answer 1

The average heat transfer coeffecient of steam condensing in a vertical tube is given as,

here first we have to find the reference temperature at which the physical properties must be calculated,

Here is the temperature of the condensing vapour. From steam table, at

Since the temperature of the wall is greater than this, I am assuming the given pressure is gauge pressure instead of absolute pressure.

So, for

The wall temperature is given as,

So,

At this temperature,

thermal conductivity of condensing water is,

Density of condensing water is

The acceleration due to gravity is,

viscosity of the condensing water,

Now the latent heat of vapourisation is not at reference temperature, it is at condensing temperature.,

Length of the tube is given as,

So,

So the average heat transfer coeffecient is 6878.05 W/m2 K